Efficiency of cell culture derivation from blastula embryos and of chimeraformation in the medaka (Oryzias latipes) depends on donor genotype and passage number

Embryonic stem (ES) cells from early vertebrate embryos only rarely retain their full developmental potential under in vitro culture conditions, but u ndergo differentiation and lose their ability for chimeric embryogenesis. T his is reflected by the fact that the ES cell technology to date could only be fully developed in mice. In the fish Oryzias latipes, the medaka, one E S-like cell line, MES1, has been established which gives rise to a high fre quency of somatic chimeras but a low degree of chimerism. Here we have test ed the effect of donor genotype and cultivation time on the efficiency of c ell culture derivation and on chimera formation. The HB12A, HB32C and HNI s trains of medaka most efficiently and reproducibly give rise to blastula-de rived cell cultures that produce pigmented chimeras in albino hosts. Seven chimeras grew to male or female adults with normal fertility, although none of them showed obvious donor germline contribution. During prolonged in vi tro propagation the frequency of chimeras and the degree of chimerism dropp ed to a value retained in the long-term cultured MES1 cells. Obviously, gen etic factors in host/donor compatibility and physiological changes during p rolonged in vitro culture may compromise, but do not abolish, the developme ntal potential of medaka ES-like cells. Thus, elucidation of conditions tha t will expand the developmental potential of medaka blastula cell cultures should lead to a further improvement towards establishment of the ES cell t echnology in medaka.